How to Bore Holes in I-Joists

You can bore relatively large holes through I-joists to run refrigerant lines, pipes and ducts.

By
Norman Becker, P.E.

May 24, 2007

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Q: I want to finish my basement but the refrigerant lines for the central air-conditioning system are fastened to the bottom of the joists. I'd like to run the lines through the joists, instead. The joists are engineered lumber shaped like an I-beam. Electrical cables already run through them, but can they accept a hole large enough for refrigerant lines?

A: Yes, you can bore relatively large holes through I-joists to run refrigerant lines, pipes and ducts. This is preferable to running the lines under the joists and then covering them with a dropped ceiling, or installing drywall over thin lumber fastened to the bottom of the joists. Running the lines through joist centers protects them. It places the lines beyond the reach of a nail or screw used to fasten drywall or to hang something from the ceiling.

Most of the relocation work is not a do-it-yourself job. You'll need to hire a heating-cooling contractor to tap the central air's refrigerant system, drain the refrigerant and capture it. After the lines are rerouted, the air-conditioning system will need to be recharged with refrigerant and checked for leaks.

You may be able to save some money by boring the joist holes--following the contractor's directions, of course. You'll also need to follow the directions of the joist manufacturer. Look on the joist's side for the manufacturer's name. The simplified drawing above is based on information for Georgia Pacific's products (gp.com), which are fairly typical.

Finally, the reinstalled lines must be properly insulated. Before the ceiling is enclosed, check the lines for gaps or damaged areas. An insulation gap can cause condensation to form at that spot and drip on the drywall below.

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